Antenna

ABSTRACT

A flat antenna for receiving digital or analogue broadcasts from a satellite, comprising at least one layer of individual receiver elements, the elements in the layer being interconnected by means of conductive paths in such a manner that the signal&#39;s phase shift owing to the position of the elements in the layer is compensated for by means of length variations in the conductive paths, where the individual receiver elements are connected in pairs to a pair collector point, the pairs are connected into sub-arrays with a sub-array collector point, the sub-arrays are connected into arrays with an array collector point, and the arrays are connected into groups with a group collector point. According to the invention the conductive paths between elements, pairs, sub-arrays, arrays and/or groups comprise one or more of the following elements: straight segments extending in a first direction, straight segments extending in a second direction perpendicular to the first direction, straight segments extending on a third direction inclined or angled in relation to the first and the second directions and bent segments or compensation leads, wherein the bent segments comprise two or more straight parts and/or one or more curved parts. The antenna comprises also reflector elements lying perpendicular to the antenna&#39;s plan dimensioned and positioned in such a way that the received signal level is considerably enhanced through constructive interference.

There is a plethora of inventions related to microstrip lines generallyand specially microstrip (also often called patch) antenna. Recentinventions relate to additional modules external to the patch antennaitself.

Either some external modules are added to existing microstrip antennadevice based on prior art technology or some additional active devicesare included such as biasing of semiconductor substrates.

The present invention is based on the following strategies:

-   -   (1) User friendliness meaning easy mounting and “plug and play”        approach, so that any layman can handle the mounting of the        antenna and connection to any commercially available tuner        without much technical effort.    -   (2) Minimising the cost of production as much as possible,        incorporating commonly available materials, which are amenable        for processing in the production of microstrip antenna and the        associated substrates and conducting materials.

With these two main points under focus, the technique described in thisinvention is based on inclusion of microstrip structures on the plane ofthe patch antenna itself and reinforcement of received signals usingconstructive interference based on positioning of reflectors on theplane of the patch antenna.

The present invention relates to a flat antenna for receiving digital oranalogue signals from a satellite, arranged to be located in asubstantially vertical position so that the antenna has an acuteinclination angle with respect to the satellite's beam direction.

Conventional flat antennae need to be in a position such that theinclination angle with respect to the satellite's beam direction is 90degrees. As the satellite's beam direction is seldom horizontal, theseantennae cannot be mounted vertically.

A normal antenna includes conductive elements (receiving units in theform of patches) arranged in various topologies of rows and columns anda network of signal feed circuits interconnecting these elements. Partof the signal feed circuit usually has microstrip structures tocompensate for phase delays in receiving the incoming radiation by theseelements. The feed circuit geometry as a whole is designed in such a waythat the signals received by selected groups of elements have the samephase before they are added together to provide a final output signal.

U.S. Pat. No. 4,963,892 shows a microwave plane antenna for receivingcircularly polarized waves. This antenna comprises conductive antennaelements and conductive paths connecting the elements together.

The conductive paths which connect the elements have different lengthsso that the main beam direction can be set in a plane including that ofthe antenna.

U.S. Pat. No. 5,66 1,494 describes a microstrip antenna for radiatingcircularly polarized electromagnetic waves comprising radiator elementswith coplanar dual orthogonal microstrip feeds. The conductive paths inthis antenna have again different lengths for phase compensation. Ifthis antenna is to be used as a receiver, the plane containing theelements of the antenna should be perpendicular to the incomingradiation to obtain a satisfactory gain.

The antenna according to the invention is specially adapted for verticalor almost vertical positioning. This is achieved by providing conductivepaths between receiving elements comprising straight segments extendingin a first direction, straight segments extending in a second directionperpendicular to the first direction, straight segments extending alonga third direction inclined or at an angle with respect to the first andthe second directions (also called slanted segments) and bent segmentsor compensation leads (these segments comprise two or more polygonalsections and/or one or more curvilinear sections). This combination ofsignal transmission paths leads to considerable improvement in the levelof received signal and makes it possible to receive satellite signals ina wide range of inclination angles with the antenna positionedvertically.

The technique used to compensate for phase delays in signals of eachelement in a group, when the antenna is mounted vertically, is based oncompensating for the signal delays in each group and element by usingthe slanted and the bent segments. The combination of these twoconducting paths, helps to receive satellite broadcasting without anyloss in signal quality, even though the antenna surface is notperpendicular to the wave fronts coming from the satellite.

Only with the bent and the slanted segments in the topology of theantenna, the antenna could be mounted vertically. Either of theseconnectors alone in the antenna topology, does not help reception ofsignals form the satellite, with the antenna mounted vertically.

The antenna according to the invention comprises individual receiverelements grouped in pairs, the pairs forming sub-arrays, the sub-arraysforming arrays and these forming groups. The conductive elements forminga pair are connected to a common point defined hereby as pair collector.The same applies for the sub-arrays, arrays and groups, where the pairs,sub-arrays and arrays will be connected to sub-array, array, and groupcollectors respectively.

The invention will more specifically comprise a flat antenna forreceiving digital or analogue broadcasts from a satellite, comprising atleast one layer of individual receiver elements, the elements in eachlayer being interconnected by means of conductive paths in such a mannerthat the signal's phase shift owing to the position of the elements inthe layer is compensated for by means of length variations in theconductive paths, where the individual receiver elements are connectedin pairs to a pair collector point, the pairs are connected intosub-arrays with a sub-array collector point, the sub-arrays areconnected into arrays with an array collector point, and the arrays areconnected into groups with a group collector point. The invention ischaracterized in that the conductive paths between elements, pairs,sub-arrays, arrays and/or groups comprise one or more of the followingelements: straight segments extending in a first direction, straightsegments extending in a second direction perpendicular to the firstdirection, straight segments extending on a third direction inclined orat an angle with respect to the first and the second directions and bentsegments or compensation leads, wherein the bent segments comprise twoor more straight parts and/or one or more curved parts. Each receivingelement has only one feed line.

In one embodiment of the invention, each pair of elements comprises onestraight segment extending in the third direction or slanted segments,that is at least one element in a pair is connected to the paircollector by means of at least one straight segment extending in thethird direction. In a preferred version of this embodiment each groupcomprises one compensation lead, that is at least one array in a groupis connected to a group collector by means of a bent or curved segment.Such segments could also be formed as meander lines.

In one embodiment the antenna is equipped with reflectors which enhancethe level of the received signal considerably, by proper dimensioning ofthe size of the reflectors and their locations. In this embodiment theantenna is equipped with reflectors for every antenna element, thereflectors being normal to the plane of the antenna. The reflectors maintask is to reflect the incident wave in such a manner that the reflectedwaves fall in the elements above each reflector and lead to constructiveinterference in all these elements, thus leading to an improved signallevel at the signal pick-up point in the middle of the antenna. Thereflectors can have design variations with perforations in the middle orat the edge of the reflectors to permit passage of radiation through thereflectors to those elements underneath them, so that the directincidence of waves on each element is sustained. The reflectors can alsobe constructed as a single reflector for each element or grouped in astrip.

The advantage of the invention is that the antenna will preferably beplaced vertically, being set at a specific inclination angle duringproduction (the angle is dependent on the degree of latitude of theplace of use and of the incoming radiation direction, e.g. in Oslo,Norway this angle is approximately 22 degrees for the most commonsatellites). A large tolerance may be allowed for on the elevation(approximately 5 degrees plus). The consequence is that an antennaproduced for optimal operation at a specific latitude will still givesatisfactory results at other latitudes. On the other hand, the apertureangle on azimuth is narrower than 3 degrees. This means that placementand adjustment of the antenna will only comprise rotating it about avertical axis until a useful signal level is received. This represents asubstantial simplification of the installation process. The installationcan thus be performed by an unskilled person.

Due to the low aperture angle, interference resulting from waves fromsatellites in close proximity to one another will be avoided. Theantenna, moreover, will not occupy unnecessary space and no dirt, snow,etc will accumulate on the surface of the antenna.

In the antenna according to the invention the phase shift between thesignals received by the various elements, as a result of differentarrival times for the signals, is compensated for, while signal loss dueto impedance mismatch introduced by the compensation devices, is kept aslow as possible.

According to the invention the length variations in the conductive pathsfor connecting the receiver elements, sub-arrays, arrays, and/or groupsare implemented in the form of bent segments and/or straight paths thatcan extend along a first, a second or a third, inclined direction. Thiswill also lead to minimisation of the loss of signal level due toimpedance mismatch in the microstrip circuits. In a special embodimentof the invention, angled, straight paths are used for connectingelements and loop links for connecting the sub-arrays, but othercombinations are also possible.

The antenna comprises two different dielectric substrates with receiverelements, one for receiving horizontally polarised signals and the otherfor receiving vertically polarised signals. Each of these two layers hasconductive paths formed as described above.

Each substrate with the conductive paths and elements has a network ofsignal delay networks and transmission paths with a mirror symmetryalong a line running across the middle of the antenna section, leadingto the centre to an air gap at which the signal will be coupled to theLNB (Low Noise Block Converter) using established techniques as found inother antennas meant for reception of satellite program transmissions.These phase compensating lines could also be formed in the form ofmeander lines.

The antenna also comprises a sheet with holes, the width of the holesbeing between 12 mm and 15 mm. The size of the holes is selected to suitthe frequency band of operation and to optimise the level of the signaland improve the signal to noise ratio. The geometrical form of the holescan also vary.

In an embodiment the antenna is in the form of a long strip, the mainreason for this being that it will be aesthetically more pleasing. Inaddition a long, narrow antenna, which is in a perpendicular uprightposition, will be able to alternate between different satellites bymeans of simple automatic adjustments, which will lead to the desiredangular displacement.

Although the different features of the antenna according to theinvention, as the compensating microstrip elements shown in FIG. 6,presence of reflectors, presence of a signal pick-up point with a gap,design variation involving a long strip of antenna array, have beenpresented as independent embodiments of the invention, an embodimentcomprising a combination of all or some of the above-mentioned featuresis also feasible within the scope of the invention.

The invention will now be explained by means of an embodiment, which isillustrated in the drawings. The example is not intended to beconsidered limiting and other combinations of elements will naturallylie within the scope of the invention. The drawings are as follows:

FIG. 1 illustrates the relative positioning of an antenna A according tothe invention and of an antenna A′ according to the prior art inrelation to a satellite beam.

FIG. 2 illustrates a first embodiment of the antenna according to theinvention in an exploded view.

FIG. 3 illustrates a second embodiment of the antenna according to theinvention in an exploded view.

FIG. 4 illustrates the position of the horizontal and the verticalpolarisation layers in one embodiment of the antenna according to theinvention.

FIG. 5 illustrates a conductive element layer with an air gap,conductive elements, sub-arrays and groups.

FIG. 6 illustrates bent or curved segments.

FIG. 7 shows the reflectors' function for reflectors withoutperforations.

FIG. 8 shows the reflectors' function for reflectors with perforations.

FIG. 9 shows one embodiment of the reflectors for each element orsub-array.

FIG. 10 shows another embodiment of the reflectors in the form of acontinuous strip meant for all the elements or array in the same row.

FIG. 11 shows possible geometries for reflector perforations. Theperforations can be located right at the edge of the reflector leadingto an opening at the edge.

FIG. 1 illustrates the relative positioning of an antenna A according tothe invention in relation to an incoming wave from a satellite S. Theantenna A according to the invention permits vertical or almost verticalpositioning (5 degrees plus from the vertical direction will still givea satisfactory signal), and the inclination angle φ will be less than 90degrees. An antenna A′ according to the prior art will be situated at 90degrees to the incoming wave.

FIG. 2 illustrates a first embodiment of the invention in an explodedview. The antenna A comprises: a sheet with holes or front cover 1, thefront cover 1 comprising holes 2 for wave propagation, a first spacer orisolation plate 3, a first conductive element layer 4 comprisingelements 5, a second spacer plate 6, a second conductive element layer 7comprising elements 8, a third spacer plate 9 and an earth plane plate10.

The first layer is a sheet of conductor 1 with holes 2. In an embodimentof the invention this sheet has 16×16 holes minus 4 in the middle, whichhave been removed, and in a second embodiment it has 8×32 holes. It ispossible to vary the number of holes 2 according to requirements (signalstrength, etc.), thus enabling the antenna to be made both larger orsmaller than the one shown in FIG. 1.

The layer 3 is a suitable dielectric material which functions as aspacer between the two conducting layers 1 and 4, at the same timeenabling the transmission of the incoming wave from the satellite to thelayers below as shown in FIGS. 1 and 2.

The first conductive element layer 4 is arranged to receive verticallypolarised signals, and is composed of a film containing conductiveelements 5, which will be discussed in more detail later.

Between the first conductive element layer 4 and the second conductiveelement layer 7 a second spacer plate 6 is placed. The function of thesecond spacer plate 6 is to provide a medium of isolation between theconductive layers 4 and 7 and suitable dielectric constant enabling thetransmission of waves.

The second conductive element layer 7 comprises antenna elements 8 forreceiving horizontally polarised signals.

The function of the third spacer plate 3 is also to provide a medium ofisolation between the conductive layers 7 and 10 and suitable dielectricconstant enabling the transmission of waves.

This special construction according to the present invention makes itpossible to mount the antenna vertical without impairing the receivedsignal quality.

This property is a consequence of the following features of the antenna:extension of the conductive path between the individual elements inpairs in order to phase-shift the signal from the upper elements so thatthey will be in phase with the lower ones (where “lower” and “upper”refer to the vertical direction), use of bent segments, use ofreflectors (which are preferably at 90 degrees but which may be arrangedat another angle) which increase the signal strength of the antenna, anduse of narrow cell holes 2 whose primary function is to reduce noise. Itis important to point out that although the presence of all thesefeatures will lead to a satisfactory result, an antenna that comprisesonly some of these elements in different combinations will also befunctional.

FIG. 3 illustrates a second embodiment of the antenna according to theinvention in an exploded view. In this embodiment a further conductivelayer 11 with holes is provided together with another isolating orspacer layer 12. The function of this conductive layer 11 with holes canbe explained through the theory of slot coupling between microstripelements and slot in the earth conductor.

FIG. 4 illustrates more precisely the general arrangement of conductiveelements 5 and 8 in the conductive layers for vertically polarisedsignals 4 and for horizontally polarised signals 7 in the firstembodiment of the antenna according to the invention as shown in FIG. 2.

FIG. 5 illustrates the first conductive path layer 4, which is arrangedfor receiving vertically polarised signals. Layer 4 comprises conductivereceiving antenna elements 5, which are connected in pairs 13 to a paircollector point 14, the pairs 13 are connected into sub-arrays 15 to asub-array collector point 16, the sub-arrays 15 are connected intoarrays 17 to an array collector point 18, and the arrays are connectedinto groups 19 to a group collector point 20. Two groups 19 areconnected to each other at a two-group collector point 21 and so on.

The second conductive path layer 7 has a similar structure containingelements, pairs, sub-arrays, arrays and groups.

The elements 5 and the sub-arrays 15 are interconnected by means ofconductive paths, and it has been shown to be particularly advantageouswith regard to loss due to impedance mismatch to arrange the paths asillustrated in the figure, viz. with straight segments along a first ora second direction x or y between the elements 5 and with bent segmentsor compensation leads between the 8-element arrays. In the shownembodiment the conductive paths between groups 19 comprise only segmentsalong the first and the second direction.

The antenna A according to the invention comprises in an embodimentfour-element sub-arrays 15 and four columns and four rows ofinterconnected sub-arrays 15, containing four groups 19 of foursub-arrays 15 as shown in FIG. 5. The number of elements in thesub-array 15 n_(s) and number of groups 19 n_(g) can be selected to suitthe applications. Similarly, the number of columns (n_(c)) and thenumber of rows (n_(r)) containing the groups can also be varied to suitthe application. The shape of each conductive element (5, 8) is selectedto match the polarisation, being vertically and horizontally orientedfor vertical and horizontal polarisation respectively. In the embodimentdescribed with reference to FIGS. 4 and 5 the characteristic numbers areas follows:

-   -   Number of elements in the sub-array (n_(s)) 4    -   Number of groups (n_(g)) 4    -   Number of columns (n_(c)) 4    -   Number of rows (n_(r)) 4    -   Number of elements (n_(e)) 16×16−4=252

The art of coupling the conductive elements (5, 8) in the sub-array 15and the sub-arrays 15 in the group 19 and placing the groups 19 in therows and columns is based on partly established antenna theory forachieving constructive interference to get maximum signal at thereceiving point in the middle of the complete antenna configuration asshown in FIG. 4, in which the antenna coupling to the receiver LNB (LowNoise Block Converter) is achieved via a field coupling mechanism placedoptimally in the vicinity of the gap between the striplines, and on aplethora of series of trials and errors in construction, tests andmodifications that led to the present state of the antenna according tothe invention.

The explanations given as theoretical basis in the description of thisinvention hence serve to describe the main principle of operation.

Generally, we can write the following equations,n _(e) =n _(g) n _(s) n _(c) n _(r)−4

As shown in FIG. 5, the distance between elements in the sub-array d_(e)and the distance between sub-arrays d_(s) the distance between groupsd_(g) are all selected to enhance the level of constructive interferenceneeded for the optimal performance of the antenna in the frequency range10.75 GHz-12.75 GHz.

A closer look into the design of the antenna as shown in FIG. 4 showsvery important variations of otherwise very linear streamlined patternsof the elements 5, 8, sub-arrays 15, groups 19, columns (C) and rows(R). The connection between the sub-arrays 15 is achieved usingconductive paths or striplines of suitable length with one segment alonga third direction pointing downwards (towards −y) to the horizontal forboth the layers of antenna meant for reception of vertically (4) andhorizontally (7) polarised transmissions. The connection between thepair of sub-arrays 15 in a group 19 is achieved by using curved or bentsegments or striplines facilitating the right phase of the signals fromthe pair of sub-arrays 15 in a group 19.

The inclination angle with respect to the transmitting satellite S(FIG. 1) being depicted by φ, we find both from measurements and theory,that the distance between rows d_(r) is equal to the distance betweenthe groups d_(g) and is given by $\begin{matrix}{d_{r} = {d_{g} = d}} \\{d = \frac{\lambda}{\sin\quad\varphi}}\end{matrix}$

FIG. 6 illustrates bent or curved segments in different embodiments. Asshown in the figure, the object of the bent or curved segments is toprovide a conductive path that does not follow a straight line, and theshown geometries are advantageous for impedance compensation.

Both conductive element layers 4 and 7 are provided with collectorelements. In an embodiment of the invention (FIG. 5) the collectorelements C have a gap G out of which the total signal from all theelements in the layer will emerge. The signal will be received by areceiving head with an input for each layer (not shown in the figures),which preferably has a point facing the gap G. It is also possible todirectly connect the receiving head, LNB (Low Noise Block Converter) tothe antenna by a soldered connection. This will then replace the pointand the gap but will not come into the same position, but will come inthe middle of the path.

The receiver elements 5, 8 in the conductive element layers 4, 7 mayhave different shapes, and may be square, round, star-shaped,triangular, etc. In a preferred embodiment of the invention the elementsare in the form of oblong squares.

The plate 10 is the earth plane used in any microstripline construction.As mentioned earlier, the horizontally and vertically polarised signalsare picked up by a suitable set of LNBs When the two films withconductive elements are placed directly above each other as explained,the two gap apertures will be slightly displaced relative to each other.The choice of vertically or horizontally polarised signal is made withthe help of LNBs and a suitable signal receiver (tuner).

With reference now to FIG. 7, an additional feature in the antenna Aaccording to the invention is the incorporation of the reflector elementR perpendicular to the plane of the antenna with a height h easilyadjustable to suit the inclination angle φ. In selected applications, toenhance the received signal, the reflector R may incorporateperforations P (FIG. 8), to facilitate transmission of the incomingwaves from the satellite S reaching the elements (5, 8) without beingblocked by the reflectors R. It is plausible to assume that theperforations function as new sources of waves just as in Huygen's wavetheory. The principle of operation can be explained as follows.

The reflectors enhance the signal quality considerably. The perforationsin the reflectors, help wave transmission to all elements, when theantenna is positioned at angle φ to the vertical as shown in FIGS. 7 and8. The reflector surfaces, act as additional sources, the phase of whichhas to be harmonised with the direct signals falling onto the elementsof the patches. The maximum path covered by the reflected wave is hcosec φ, the patch should be placed within a distance of h cot φ. Thewave leaving the reflector after reflection will be reaching the patcharea after a maximum delay of h/c sin φ. For the bandwidth of operationof the antenna, these values have to be taken into account in selectingthe size of the patch and that of the reflector.

The receiving quality of the antenna with the plane of the antenna invertical position is possible with the connecting lines as shown inFIGS. 4 and 6. The reflector is not necessary for the operation of theantenna with its plane positioned vertically, but enhances the receivedsignal level.

FIGS. 9 and 10 show different embodiments of the reflectors formed assingle reflectors (FIG. 9) or grouped in a strip (FIG. 10).

FIG. 11 shows possible geometries for reflector perforations.

As stated before, the antenna according to the invention provides asimple answer to a long felt need by providing an easy to manufacturedevice which can be mounted on a vertical wall and tuned by an unskilledperson.

1-9. (canceled)
 10. A flat antenna (A) for receiving digital or analoguebroadcasts from a satellite (S), comprising at least one layer ofindividual receiver elements, the elements in the layer beinginterconnected by means of conductive paths in such a manner that thesignal's phase shift due to the position of the elements in the layer iscompensated for by means of length variations in the conductive paths,where the individual receiver elements are connected in pairs to a paircollector point, the pairs are connected into sub-arrays with asub-array collector point, the sub-arrays are connected into arrays withan array collector point, and the arrays are connected into groups witha group collector point, characterized in that the conductive pathsbetween elements (5,8), pairs (14), sub-arrays (15), arrays (17) and/orgroups (19) comprise one or more of the following elements: straightsegments extending in a first direction, straight segments extending ina second direction perpendicular to the first direction, straightsegments extending on a third direction inclined or angled in relationto the first and the second directions and bent segments or compensationleads, wherein the bent segments comprise two or more polygonal sectionsand/or one or more curvilinear sections.
 11. Antenna according to claim10, characterized in that at least one sub-array (15) in an array (17)is connected to the array collector (18) by means of at least onestraight segment extending in the third direction.
 12. Antenna accordingto any of the preceding claims, characterized in that at least one array(17) in a group (19) is connected to a group collector (20) by means ofa bent segment,
 13. Antenna according to claim 10, characterized in thatit comprises layers of elements (8) for receiving horizontally polarisedsignals and layers of elements (5) for receiving vertically polarisedsignals.
 14. Antenna according to claim 10, characterized in that itcomprises reflector elements (R) situated in an angle to the antennaplane, where this angle is preferably 90 degrees.
 15. Antenna accordingto claim 14, characterized in that it is equipped with individualreflectors (R) for the individual antenna elements (5,8) or with a stripof reflectors (R) assigned to several elements.
 16. Antenna according toclaim 14 or 15, characterized in that the reflector elements orindividual reflectors (R) comprise perforations (P) where theseperforations to facilitate transmission of the incoming waves from thesatellite (S) reaching the elements (5, 8) without being blocked by thereflectors or reflector elements (R).
 17. Antenna according to claim 10,characterized in that each conductive element layer (4,7) comprises acollector element (C) for signals from all the antenna groups (19), andthe collector element (C) consists of a conductive path with an air gap(G), where path length is different on both sides of the gap (G), and areceiving head for receiving signals from the gaps.
 18. Antennaaccording to claim 10, characterized in that it comprises a sheet (1)with holes (2), the width of the holes (2) being between 12 mm and 15 mmfor the frequency band of operation.
 19. An antenna according to claim10, characterized in that it is in the form of a strip.